Electrical switch contacts



Patented Nov. 16, 1937 PATENT OFFICE ELECTRICAL SWITCH CONTACTS Lyall Zickrlck, Schenectady, N. Y., asslgnor to General Electric Company, a corporation oi New York No Drawing. Application May 20, 1937, Serial No. 143,762

Claims.

The present invention relates to electrical switch contacts and more particularly to contacts adapted for use in circuit, breakers in which thecontacts are subject to sudden heavy 5 inrushes of current. In the supply of a lighting load for example the resistance oi the cold filaments is very low and permits an initial inrush of current which may be ten times higher than the normal current and suficienhto cause the circuit breaker contacts to become welded together.

It is an object of the present invention to provide a switch contact which resists welding under heavy initial inrushes of current, is relatively inexpensive and does not oxidize readily.

The novel features which are characteristic of my invention are set forth with particularity in the appended claims. My invention itself however will best be understood from reference to the following specification.

In carrying out my invention, I employ an alloy which consists substantially of silver, copper, cadmium and lead. The preferred composition contains about 57.5% silver, about 22.5% copper,

about 17% cadmium and about 3% lead. In the fabrication of switch contacts 'the alloy is cast into rods which, if desired, may be swaged to a required diameter. The contacts are then cut from the rod and usually in the form of a rivet whereby they may be readily secured to a sup" porting member. Contacts of the above composition and about thick have been operated on a 110 volt, cycle system having an initial inrush of current or 320 amperes. Under such 88 conditions the switch contacts have been given about 20.000 operations, or enough to wear out The cadmium content of the alloy may vary from about 12% to 27% and the lead content irormabout 1, to 10%, silver, or silver and copper in the relation of about 72 parts or silver to 28 parts of copper, constituting the remainder of the alloy. The best results however will be obtained by the use of 17% cadmium and 3% lead.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. -A switch contact containing about 1 to 10% lead, about 12 to 27% cadmium, the remainder consisting substantially of metal from the group silver and copper.

2. A switch contact containing about 1 to 10% lead, 12 to 27% cadmium, the remainder consisting mainly of silver but comprising an appreciable quantity oi copper.

, 3. A switch contact consisting of about 57.5% silver, about 22.5% copper, about 17% cadmium and about'3% lead.

4. A switch contact containing about 1 to 10% lead, 12 to 27% cadmium with the remainder silver.

5. A switch contact consisting of about silver, 17% cadmium and 3% lead.

'thecontacts, without giving any indication oi welding action,

LYA L L- shaman 

